95 suburban Idle problem (long)

Here is one for the books!!

I have a 95 chevy suburban, 134k, 5.7L, 4x4, TBI. Engine is clean, no leaks(lower rear main only). 2 years ago the water cooled manifold nipple broke and the intake had to be removed to fix(replace). While intake was off, the EGR valve was remove and location was cleaned of built up carbon. Replaced intake with new intake gaskets and used Permatex sealant on the front and rear between the manifold and engine(per instructions). Installed Distributer (had marked before removal) by lining up marks, and had the engine timed by "ear and power braking" by old gm mechanic. Broke the coolant sensor (front of engine) and replaced with (autozone)part still a high idle, took to dealer service and the scan showed a -35 degree teperature, replaced with $22 GM part (no problem). Engine idled at 550 in drive and about 700 in neutral. No power problems and had a mpg of 15-17 on the highway. There isn't any smoke and had no detonation problems. Oil changed every 2500 since owning at 91K.

NOW the problem ... Engine developed a small miss of about 50 rpm miss. Has gotten progressively worse. I did replace a pcv to TBI HOSE and got a perfect idle for 3 days. Now the rpms in drive are at 500 and idles with every 5 seconds a 1-250 rpm loss and will eventually die. It does the same at a red light,turn etc. It also sounds like pinging-detonation while cold (below 150 degrees) and accelerating. Also has surged at times at red light and does die out. The plugs are ac delco and the wires are delphi - 6 months old.

What have I done... Taken out the TBI after market spacer and have put in a new IAC. Pull of the hose to the MAP sensor and got a distinct change in the engine, cut out, and had a lot of vacume. Removed the TPS connector and got a check engine/service light...removed neg terminal and reset computer. THERE ARE NO CODES SHOWING (jumped connector under dash). Removed vacume hose off of EGR and got no code, light or change in idle. Removed IAC connector and also received no change in idle nor did I get a check light.

Does anyone have a possible solution.....The dealer says worn cam lobes(#7 cyl), injectors, gasket leaks...etc. If it was a cam the miss would be consistant and the miss(lope) would not have disapeared when I changed the pcv valve hose to tbi. Injectors "look ok" but no test done...Have done the old test of pouring a "VERY" slight amout of water and then trans fluid into TBI at raised rpms to burn out carbon.....

HELP !!!!!!!!!!!!!!

2 things to look at are:

1) Pick-up coil in the dist. If it is yellow and flaking apart, then it is bad.

2) Upper shaft bushing in the dist. Take off the cap and try to move the rotor, if the shaft moves, the bushing needs to be replaced (or replace the dist).

//2000CAYukon

Here is what I did to fix my problem. On 11 Jan 05, I replaced the IAC with no results positive. Today after I read more posts, I went and bought the following items, Cap and rotor($22), TPS($21) and coil pickup($28) and fuel filter($5) and new TBI gasket($7). I replaced the fuel filter, then pulled the Dist. Cap off. In doing this I pulled off the coil wire....The coil looked like a corroded battery terminal. I cleaned off the coil with sandpaper and bought a set of 8mm accel high temp wires(#9020 $80). I cranked up the vehicle and it runs perfect!! The idle in N or P is about 650-700 and the idle in drive is 550 to 600. No miss what so ever. I also replaced the TBI gasket...... So I will return the coil pick up and TPS tomorrow. I would have never thought about the Coil being corroded. I had replaced the wires with autolites 6 months ago!! Must have gotten wet when I was cleaning my engine with a pressure washer(regular cleaning -every 3 months)... The dealer was very adamant about putting the vehicle on the scan for $89...rip off!!! Even after I told them what the problems were they kept insisting it was cam lobes and that I had a lot off miles on my engine(134K).... Hope this helps others......Here is my email...PPPaciera @ hotmail.com

Glad you found your problem. A little dielectric grease at the end of the plug wires and coil wire will keep water out and help prevent corrision.

//2000CAYukon

Hi, I too have a 95 Suburban (98K miles) with an intermitant low speed idle problem. After reading the threads, I replaced the cap, rotor and plug wires. The idle problem went away, Thanks alot. I had taken it to a mechanic who checked the codes (there were none), then cleaned the IAC and TBI injection. Then he replaced the IAC motor and it still stalled. He was at a loss at that point. Thenks again for the great info.

Daniel Denney